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What sense of smell – odors – tells us about mental illness?

Posted May 13 2013 5:00am

Is there a connection between sense of smell and mental illness?

Improving memory

There is a body of research that tells us that there is a connection between sense of smell, your ability to recognize and identify odors and the chance you have or will develop a mental illness. There are also cases of olfactory hallucinations; smelling things that everyone else is sure is not there.

While this research suggests some connections, to me the articles I have read are short of conclusive.

An altered sense of smell has been linked to disorders as divergent as Schizophrenia, Bipolar disorder, autism and eating and feeding disorders.

One thing we do know is that the ability to identify an odor is not the same thing as the ability to detect one. People are more likely to like a smell they can identify and unknown smells are more likely to be considered unpleasant. Memory and its connection to smells are important for many reasons.

This is significant because smells are powerful memory cures. People who have poor ability to notice smells or to remember them are at a disadvantage in remembering things that might be associated with those smells.

The disorder most cited as having olfactory (odor or smell) impairment is Schizophrenia. More interesting yet is the repeated observation that males with schizophrenia are far more likely to have olfactory disruption than females (Nguyen et al, 2010.) These males with schizophrenia had disruption of odor identification, memory, odor detection abilities and poor odor discrimination, the ability to tell one smell from another.

Females in these studies rather than not being able to recognize or identify smells were more likely to smell foul or unpleasant things that were in fact not detectable to others. The conclusion was that women have more olfactory hallucinations and men more loss of ability to smell. 

Schizophrenia is characterized by negative symptoms, which are the loss of some abilities others have, as well as positive symptoms such as hallucinations. Someone with schizophrenia will likely have or experience social withdrawal, attention problems, difficulty making decisions, and perceptual problems.

People with schizophrenia also have high rates of olfactory identification problems, discrimination of smells, olfactory memory and olfactory detection errors, principally in males. Poor olfactory discrimination is also found in close relatives of people who have been diagnosed with schizophrenia even when those relatives have not received the diagnosis themselves.  

Olfactory identification problems do not appear to be found in people with Bipolar disorder, Major depressive disorder, other related psychosis or anorexia nervosa.

Olfactory hallucinations and discrimination deficits are seen in those with Alzheimer’s, and Parkinson’s diseases in addition to Schizophrenia.

One researcher reports that people with Bipolar disorder have some olfactory impairment but that they are less bothered by unpleasant smells that those people who have Schizophrenia (Cummings et al., 2010.)

In Autism olfactory identification is reported as impaired. Individuals who had been diagnosed with Autism preferred Lemon and Orange smells to lavender. They disliked most other strong smells. In Autism strong smells are linked to perceptions of taste and result in high rates of food refusal and selectivity (Hrdlicka et al., 2010.)

One condition of note is olfactory hallucinations. Some patients reported a foul smelling order coming from themselves. This odor was not detected by staff. This olfactory hallucination is referred to as Reference Syndrome and was reported in patients with temporal lobe epilepsy. Other olfactory hallucinations have been reported in clients with substance induced Psychotic disorder, Hypomania with Alcohol dependence combined with hypomania (Luckhaus et al., 2003.)

There does not appear to be any connection between depression and olfactory dysfunction (Scinska et al., 2008.)

Olfactory disregulation has also been linked to people who have frequent migraines, with over 45% of people experiencing migraines reporting odors are triggers for those migraines. In migraine suffers almost 25% had a fear of a particular odor and an equal number reported taste abnormalities when having a migraine episode. MRI’s showed that women were eight times more likely to have brain activation from odors. This makes one wonder if many of the issues with odor detection, memory and discrimination are more linked to gender than to a particular psychiatric diagnosis.

Other studies have reported significant episodes of visual hallucinations during migraine attacks and make the point that visual and auditory hallucinations are so pronounced and readily identifiable most people are not asked about and do not report either olfactory or gustatory (taste) hallucinations.

In people with schizophrenia 75% reported auditory hallucinations, 37% reported somatic hallucinations while olfactory hallucinations were reported by 18% of the patients which is slightly more than the 14% who reported visual hallucinations. Despite being so common, few clients report olfactory hallucinations and clinicians are not generally looking for them.

While people with schizophrenia may experience hallucinations in all modalities, providers frequently stop asking about hallucinations after the first or second reported hallucination.

Researchers find that people who report being under “stress” are more likely to have experienced olfactory hallucinations and one study concludes that stress may lower the threshold for hallucinations of any type.

Because the major part of the olfactory sensing part of the brain is on one side of the brain researchers have suggested that there may be a difference in the way in which left-handed and right-handed people experience olfactory hallucinations.

While olfactory hallucinations are readily identifiable in people who have migraines they are less identifiable but more likely to be described as unpleasant in those with epilepsy.

While we still can’t use olfactory or gustatory hallucinations or dysfunction as makers for a particular mental illness, we know abnormalities in the sense of smell and taste may be factors in the development of a mental or emotional problem.

Have you experienced an alteration in your sense of smell or taste and no medical reason has been found? Care to share?

David Miller, LMFT, LPCC 

For more about David Joel Miller and my work in the areas of mental health, substance abuse and Co-occurring disorders see the about the author page . For information about my other writing work beyond this blog there is also a Facebook authors page, up under David Joel Miller. Posts to the “books, trainings and classes” category will tell you about those activities. If you are in the Fresno California area, information about my private practice is at

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